Suction forming roll n double screen method and machine for the manufacture of a fibrous material web

ABSTRACT

A wet section ( 10 ) of a paper or cardboard machine and a process for the manufacture of a fibrous material web are suggested. The wet section ( 10 ) exhibits a double-screen segment (US), in which two screens ( 16, 18 ) are guided about parallel to one another and into which a fibrous material suspension ( 27 ) is introduced. The double-screen segment (US) is looped around a roll ( 22 ). The means ( 30, 32, 38 ) for the immobilization of the fibrous material suspension in the double-screen segment (US) are provided on the roll ( 22 ), for the formation of the fibrous material web. Moreover, the wet section exhibits means ( 32, 34, 36; 34, 36, 66 ) for further draining of the fibrous material web. 
     The roll ( 22 ) is thereby a combined forming and draining roll ( 22 ), which exhibits a forming sector (FS), on which the immobilization means ( 30, 32, 38 ) are arranged, as well as a draining sector (ES) located in the direction of the running screen behind the forming sector (FS), on which at least a predominant part of the draining means ( 32-36; 34, 36, 66 ) is arranged.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a wet section of a machine to manufacture afibrous material web, especially a paper or cardboard web, with adouble-screen segment, in which two sieves are guided approximatelyparallel to one another and into which a fibrous material suspension isguided, a roll, around which the double-screen segment is looped;apparatus arranged on the roll for the immobilization of the fibrousmaterial suspension in the doublescreen segment for the formation of thefibrous material web, and apparatus to further drain the fibrousmaterial web.

2. Discussion of Background Information

Furthermore, the invention relates to a method for the manufacture of afibrous material web, especially a paper or cardboard web with the stepsto guide two screens in a double-screen segment approximately parallelto one another and around a roll, to introduce a fibrous materialsuspension into the double-screen segment, to immobilize the fibrousmaterial suspension on the roll in the double-screen segment whileforming the fibrous material web, and to drain the fibrous material webfurther.

Such a wet section and a method of this kind for the manufacture of afibrous material web are generally known, e.g., from EP-A-0 607 549.

In the present context, a wet section is to be understood as the sectionlocated before the drying section of a paper or cardboard machine, thatis normally the arrangement of head box, screen section, and presssection. It is given that especially the screen section and the presssection do not necessarily have to lie in sequence behind each other.So, for example, pressing elements can be contained in the actual screensection.

The wet section bears particular significance in the manufacture ofpaper webs. In the wet section, the immobilization of the fibrousmaterial suspension, which has been supplied in fluid form, takes place.The fibers which initially float freely in the suspension thereby are“immobilized” relative to one another via the removal of water. Prior toor during the immobilization, irregularities which appear can becompensated only insufficiently or not at all through subsequentsections of the paper machine.

The construction of such a wet section is typically a compromise betweendifferent, competing demands, including web run speed, web width,regularity of the characteristics of the finished paper web, surfacequality, as well as compactness of the machine, the lowest possibleinclination toward contamination, easy access for cleaning, as littleexpense as possible, etc.

Double-screen segments are used in wet sections in so-called gap-formersas well as in so-called hybrid-formers. Two continuous screens areguided thereby over a segment, the double-screen segment, parallel toeach other.

In gap-formers, the two screens are guided over a forming roll as asupport body, with the fibrous material suspension being introduced froma head box into an opening formed by the two screens and lying near tothe forming roll.

In known wet sections, the two screens are guided over another segmentparallel to one another following the looping around the forming roll;typically, forming strips and/or draining media such as suction boxesare arranged in this other segment in order to assist the draining ofthe fibrous material suspension, i.e., the “immobilization,” or thefurther draining of the fibrous material web in this other segment; seefor example EP-B-0 489 094.

The noted forming strips preferably are pressed flexibly onto one of thetwo screens, each with a force which can be selected. It is therebypossible to optimize the so-called formation (transparency) in thefinished paper.

The screen section known from EP-B-0 489 094 has a very big length,however, and exhibits a large number of individual parts.

Furthermore, a wet section in the prior art is disclosed in the Germanpatent application 196 34 995.8.

In this wet section, similar to that in EP-A-0 607 549, an upper screenand a lower screen are looped around a forming roll and hereafter guidedparallel to each other to a screen-suctioning roll, which serves furtherdraining of the formed fibrous material web after the immobilization. Inthe vicinity of the suctioning zone of the screen-suctioning roll, theupper screen is lifted from the web, so that the fibrous material webremains on the lower screen.

In EP-A-0 607 549, mentioned at the outset, the two screens are guidedparallel from the forming roll to a screen-suctioning roll which servesthe further draining of the web. In the vicinity of its suctioning zone,the outer screen is lifted from the web and the inner screen so that theweb remains behind the double-screen segment on the inner screen.

SUMMARY OF THE INVENTION

The problem which forms the basis of the invention consists thus ofindicating a wet section which is compact, inexpensive to manufacture,and can be maintained cost-effectively.

This problem is solved with the wet section noted at the outset in thatthe roll is a combined forming and draining roll, which exhibits aforming sector, on which the immobilization media are arranged, as wellas a draining sector located in the direction of the running screenbehind the forming sector; at least a predominant portion of thedraining media are arranged on the draining sector.

The problem is also solved with the process noted at the outset for themanufacture of a fibrous material web, moreover, in that theimmobilization occurs in a forming sector of the roll and at least apredominant part of the subsequent draining occurs in a draining sectorof the roll located in the direction of the running screen behind theforming sector.

The problem is completely solved in this way.

With the invention, a so-called “mono-suctioning roll” former isrealized. Departing from the previous basic concept of wet sections, inwhich only the immobilization or a part of the immobilization processoccurs on a forming roll, in accordance with the invention not only theimmobilization of the fibrous material suspension is attained on thecombined forming and draining roll, but also a substantial, additionaldraining of the likewise formed fibrous material web. Thus, the fibrousmaterial web, running from the combined forming and draining roll(below, combination roll), can, if necessary, be transported directlyinto a press section or even directly into a drying section. Hereby, amultiplicity of individual elements, especially an additionalscreen-suctioning roll, is spared. The wet section in accordance withthe invention can hereby be manufactured more cost-effectively arid isextremely compact. Fewer replacement parts must be provided duringoperation, so that even the maintenance of the wet section is especiallycost-effective. Because for the maintenance of wet sections, a reserveroll must be kept available for every type, in order to minimize machinedown times. With the wet section in accordance with the invention, onlythe combination roll thus must be provided in duplicate, and notrespectively a combination roll and an additional screen-suctioningroll. The single combination roll enables large web widths and high beltrunning speeds.

Preferably, the outer screen facing away from the roll is guided so thatit is lifted in the vicinity of the draining sector away from thefibrous material web.

The fibrous material web, formed and drained further, remains on thescreen facing the combination roll. Following this it can be conveyeddirectly or after a suitable diversion into another section of the papermachine.

Since the combination roll in the draining sector always exhibitssuctioning segments for draining, one of the same can be used as aseparating suctioning segment (as with known, conventional suctioningrolls).

With a preferred embodiment, the fibrous material web exhibits a drycontent of at least 10%, and preferably at least 12%, in the area of itsrunoff from the combination roll.

In conventional forming rolls, the dry content of the fibrous materialsuspension or web in the runoff area always lies 4-7%. By providing adraining sector on the combination roll in accordance with theinvention, the dry content of the fibrous material web can be increasedsignificantly in the area of the runoff from the combination roll, apredominant portion of the subsequent draining of the fibrous materialweb occurring after the immobilization on the draining sector. Hereby itis possible to transport the fibrous material web directly into a presssection or even into a drying section of the paper machine. In any case,only a few more draining elements are necessary from the discharge areaof the combination roll to another section of the paper machine.

Preferably, the outer screen facing away from the combination roll islifted by means of a screen guiding roll from the fibrous material web,whereby the screen guiding roll is designed to be adjustable, in orderto adjust the length of the double-screen segment.

Hereby it is possible to change the length of the double-screen segmentand in particular, that of the draining sector, in order to adapt thewet section to various paper grades and to various types of paper stocksupplied. In a stock which can be drained easily, one will lift theouter screen facing away from the combination roll early on, in order tokeep the remoistening of the formed fibrous material web from the outerscreen low. By contrast, with material which is difficult to drain itwill be necessary to keep the outer screen on the fibrous material weband the inner screen facing the combination roll for a relatively longtime. Otherwise, the outer screen can carry a certain portion of thefibrous material web with it.

It is furthermore preferred if the fibrous material suspension isintroduced into the double-screen segment by means of a head box and ifthe head box is arranged so that the fibrous material suspension flowsout against the force of gravity.

On the one hand, the head box idling at the transitory down time of thewet section is avoided hereby. Thus, distortion of the head box isavoided above all through the lack of the typically heated fibrousmaterial suspension. A distortion results in a loss in valuable timeuntil the head box assumes the correct form during a restart.

In an advantageous development of the invention, the combination rollexhibits at least one draining suctioning section in the draining sectorfor the draining the fibrous material web.

Via such a draining suctioning section, it is guaranteed that adraining—against centrifugal force—can ensue through the screen facingthe combination roll.

It is thereby especially preferred if the combination roll exhibits amultiplicity of draining suctioning segments.

A multiplicity of draining suctioning segments allows a largevariability with respect to the suctioning capacity. In other words, thesuctioning capacity can be adjusted variously in a simple, constructivemanner via the draining sector with this embodiment of the invention.

It is preferred, furthermore, if the suctioning capacity of the drainingsuctioning sections in the direction of the running screen is largerfrom section to section.

Via this measure, the suctioning capacity is adapted optimally to thesuction requirement, since the water content of the fibrous materialsuspension decreases over the length of the draining sector, so that thedraining resistance becomes greater. In other words, the higher the webdry content becomes, the higher the air speed must be in order to stillbe able to remove water from the web by means of vacuum pressure.

At the same time, it is especially preferred if a vacuum pressure of 0.6to 0.99 bar absolute is applied to a first draining suctioning section,a vacuum pressure of 0.3 to 0.7 bar absolute to a second drainingsuctioning section, and a vacuum pressure of 0.2 to 0.4 bar absolute toa third draining suctioning section.

It is preferred, moreover, if the draining suctioning sections extendover a sector of the combination roll from 60° to 150°, especially 70°to 90°.

Hereby one attains a sufficient length of the draining sector inconnection with a corresponding diameter of the combination roll, inorder to drain the fibrous material web at the combination roll enoughso that the formed fibrous material web can essentially be transferredwithout additional draining means to a subsequent press section ordrying section.

It is especially preferred if the roll in the forming sector exhibits atleast one forming suctioning section.

Via this measure, a draining of the fibrous material suspension isattained not through the outer screen facing away from the combinationroll alone, but also through the inner screen. The “forming capacity” or“forming speed” can be increased hereby. In other words, theimmobilization of the fibrous material suspension can be attained in ashort period of time or via a comparatively short forming sector.

At the same time, it is preferred if a vacuum pressure of 0.7-0.99 barabsolute is applied to a first forming suctioning section.

Such a value enables a sufficiently strong draining of the still largelyfluid fibrous material suspension on the one hand. On the other hand,this value is not so high that the quality of the finished fibrousmaterial web is negatively affected.

Preferably, the forming segment(s) extend(s) over a sector of the rollfrom 20° to 100°.

It has been observed that a complete immobilization of the fibrousmaterial suspension can be attained within such a sector, especiallywhen the diameter of the combination roll is large.

In accordance with a particularly preferred example, the jacket of thecombination roll is designed as a reservoir for the water taken from thefibrous material suspension or web.

Via this measure, it is possible, on one hand, to drain the fibrousmaterial suspension or web to match demand. On the other hand, it is notnecessary to remove a larger volume flow of water continuously via theinside of the combination roll. If the combination roll is suctionedover the entire looping area of the two screens, at least a considerableportion of the water remains until behind the last suctioning section inthe combination roll jacket. Afterwards, the water is spun out of thejacket due to centrifugal force. Thus, the kinetic energy of thecombination roll is utilized in an advantageous manner, in order toagain divert the water extracted from the fibrous material suspension orweb. The performance requirement of the wet section in accordance withthe invention can be decreased hereby. It is self-evident thereby thatin the spin-off area behind the last suctioning section, an accordinglydimensioned collection box preferably is provided, in order to collectthe water spun off.

It is especially preferred if the combination roll is fitted with asuctioning unit which produces an air flow volume that is sufficient tosuction essentially all the water extracted through the inner screenfrom the fibrous material suspension or web into the jacket of thecombination roll.

Hereby, it is attained in a structurally simple manner that the drainingof the fibrous material suspension or web can ensue both through theouter screen, due to centrifugal forces, as well as through the innerscreen. Insofar as the outer screen is already lifted from the fibrousmaterial web in the area of the draining sectors, a further drainingensues alone via the inner screen.

It is especially preferred if the suctioning unit diverts the air flowvolume to both front ends of the combination roll.

It is attained hereby that the velocity of the flow of air volume—with agiven suctioning cross-section—is reduced significantly. Each front endthus “services” about half the machine width of the combination roll,for example.

It is preferred, furthermore, if the combination roll does not exhibitits own drive.

Hereby, a suctioning-off to both front ends of the combination roll canbe realized in a particularly simple structural manner.

In accordance with another preferred embodiment, at least one formingstrip, which can be flexibly pressed to the outer screen facing awayfrom the roll, is arranged in the forming sector.

Hereby, the “formation” of the finished paper web can be significantlyimproved; i.e., the fibers are distributed in the web more uniformly.

At the same time, it is particularly preferred if the forming strip(s)on the outer screen is (are) arranged opposite the forming suctioningsection(s) of the combination roll.

Via the combination of a forming suctioning segment on the combinationroll and a forming strip opposite the forming suctioning segment, theimmobilization of the fibrous material suspension can ensue particularlyquickly and effectively. Through the forming strip, which can be appliedin a flexible manner, pressure impulses can be introduced into thefibrous material suspension, whereby fibrous clumps which maypotentially form are dissolved. This leads, on the one hand, to aneasier water removal and, on the other hand, to a more even distributionof the fibrous materials in the finished fibrous material wet).

It is particularly preferred if a row of 3 to 15 forming strips, andpreferably 5 to 8, is arranged over the forming sector.

It is preferred, furthermore, if on the outer screen facing away fromthe combination roll, the water collection box is arranged extendingitself approximately over the entire double-screen segment.

It is possible, hereby, to collect the water escaping through the outerscreen.

It is preferred, furthermore, if another water collection box isarranged on a peripheral segment of the combination roll, which islocated behind a last suction segment.

In this other water collection box, the water stored in the jacket ofthe combination roll can be extracted and collected.

Via the water collection boxes, a contamination by water of theremaining parts of the wet section or by “fog” appearing by atomizationeffects is largely hindered or completely eliminated. Overall, theinvention enables a construction style in the so-called “clean design.”

At the same time, preferably, at least one water collection box isarranged such that water is collected essentially due to the force ofgravity alone.

It is possible hereby to collect and divert the water spun out, withouthaving to provide a vacuum chamber. This brings with it considerablesavings in energy. It is particularly preferred if one water collectionbox, assigned to the double-screen segment, as well as another watercollection box, arranged behind the last suctioning section, arearranged in this manner, for example, on opposite horizontal sides ofthe combination roll.

It is of particular advantage, if the diameter of the combination rollis greater than 1.5 m, and in particular, greater than 2 m.

Such a diameter enables the formation of sufficiently long forming anddraining sectors with relatively small angles of belt contact of the twoscreens around the combination roll. In addition, the centrifugal forceacting upon the water (streaming inside through the roll jacket) isrelatively small; the specific draining capacity (according to surfaceunit) is consequently relatively large. In other words, it can beguaranteed that the fibrous material web is drained sufficiently enoughat the end of the draining sector, in order to be transferred to asubsequent section of the paper machine.

Furthermore, surprisingly, it has been shown that the disadvantage of amore elaborate construction of a combination roll with an accordinglylarger diameter is compensated much more by the advantages that can beattained.

In accordance with another preferred embodiment, at least oneextended-nip press device is arranged on the outer belt facing away fromthe combination roll in the draining sector.

Via the measure of providing a pressing device already on thecombination roll, the fibrous material web running off the combinationroll can have a much higher dry content. The combination roll is thusconstructed as a combined forming, draining, and press roll. Theattainable dry content of the fibrous material web which can be targetedcan be sufficient to transfer the fibrous material web directly onto aconventional drying section.

In accordance with a preferred embodiment, the extended-nip press deviceexhibits a shoe press roll, whose mating roll is the combination roll.

In contrast to traditional extended-nip press devices, a roll is herebyspared. Moreover, it results in a high savings potential in guide rolls,suctioning rolls, etc., for otherwise typical transfer belts from thescreen section into the classic pressing section. A shoe press roll isparticularly suited because on one hand, the pressure exerted isadjustable and on the other, the friction losses are low, since thejacket of the shoe press roll runs corresponding to the belt velocity.

At the same time, it is particularly preferred if the outer screen islooped around the shoe press roll, so that it is lifted from the fibrousmaterial web.

The shoe press roll thus simultaneously acts as a guiding roll for theouter screen. Because of the draining suctioning section lying opposite,the fibrous material web remains securely on the inner screen.

In accordance with an alternatively preferred embodiment, the shoe pressroll is arranged behind the double-screen zone on the combination roll.

It is an advantage that the guiding roll for the outer screen facingaway from the combination roll can be designed so as to be displaceable;that is, the length of the doublescreen segment can be adjustable.Moreover, it is possible to eliminate a separate press felt inside theloop of the outer screen. Thereby a construction can be attained whichis easy to manage and uncomplicated.

At the same time, it is particularly preferred if a belt is loopedaround the shoe press roll, by means of which the fibrous material webis taken from the inner screen facing the roll.

Though this measure, it becomes possible to eliminate a separate take-uproll for the removal of the fibrous material web from the inner screen.Overall, a wet section results which is particularly compact andcost-effective to make.

In an alternative embodiment, it is preferred if a belt is looped aroundthe shoe press roll, the band being removed just behind the shoe pressroll from the fibrous material web, whereby the fibrous material web isremoved behind the shoe press roll from the screen facing the roll.

In this alternative embodiment, the remoistening of the fibrous materialweb behind the shoe press roll the belt looped around the shoe pressroll can be avoided. This is because the moistened belt (typically afelt) is removed just behind the shoe press roll by means of a separatetake-up roll, typically. The fibrous material web is thus removed fromthe combination roll by an additional—dry—take-up belt, which is loopedaround the separate take-up roll.

It is particularly preferred if no other press devices are providedbetween the runoff point of the fibrous material web from thecombination roll and a transfer point of a drying section.

It is possible hereby to make an especially compact wet sectionavailable, which assumes both the function of a traditional screensection as well as the function of a conventional pressing section.

It is particularly preferred that the wet section in accordance with theinvention is used for the manufacture of graphics paper with a surfaceweight of 30 to 110 g/m².

It is to be noted generally that felts or a felt/screen combination canalso be used in place of screens. The head box can beconsistency-controlled, in order to be able to influence the crossdirectional profile.

It is self-evident that the features noted above and those below yet tobe explained can be used not only in the combination respectively given,but also in other combinations or in isolation, without leaving thescope of the present invention.

Embodiment examples of the invention are depicted in the figures of thedrawings and are explained in more detail in the followingspecification.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic side-view of an embodiment of a wet section inaccordance with the invention;

FIG. 2 shows a schematic depiction of the combination roll to explainthe nomenclature used;

FIG. 3 schematically shows a head box which is consistency-controlled toinfluence the cross directional profile; and

FIGS. 4 through 10 show schematic side-views of other embodiments of awet section in accordance with the invention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The first embodiment of the wet section in accordance with the inventionis generally noted in FIG. 1.

The wet section 10 exhibits a head box 12 and a screen section 14.

The screen section 14 exhibits a continuous inner screen 16 and acontinuous outer screen 18, which are guided approximately parallel toeach other in a double-screen segment US (see FIG. 2).

Furthermore, the screen section 14 exhibits a combined forming anddraining roll (in the following, combination roll) 22 in the innerscreen 16 and a breast roll 24 lying opposite in the outer screen 18.The combination roll 22 and the breast roll 24 are arranged such that anopening 26 is formed, into which a fibrous material suspension 27 isintroduced from the head box 12 diagonally from below, so that thefibrous material suspension 27 flows out against the force of gravity.

The combination roll 22 exhibits four consecutive suctioning sections30, 32, 34, 36. The first suctioning section 30 starts about at thewinding-on point of the outer screen 18 onto the combination roll 22.The third suctioning segment 34 ends about in the area of the runoff ofthe outer screen 18 from the combination roll 22. The fourth suctioningsection 36 extends to the area of the runoff of the inner screen 16 ofthe combination roll 22.

The four suctioning sections 30, 32, 34, 36 lie in a row locally fixedin the machine direction of the screens 16, 18 directly. The foursuctioning sections 30, 32, 34, 36 extend over a sector FS+ES, asdefined in the nomenclature from FIG. 2; that is, they expand across aso-called forming sector and a so-called draining sector.

The forming sector FS is that sector in which the immobilization of thefibrous material suspension takes place. The forming sector FS ends on aline; this appears in the illustration as point E, in which theimmobilization of the fibrous material suspension is closed. At thepoint E, the draining sector ES begins, in which the fibrous materialweb, formed by the immobilization, is further drained. The sectors FSand ES preferably lie directly behind one another, with the line ofseparation being formed by point E. They can, however, also be spacedapart in such a manner that between the forming sector FS and thedraining sector ES no draining takes place. One can imagine that thescreens converge toward each other up to point E, which is drawn inexaggeration in the illustration.

Moreover, it is to be perceived from FIG. 2 that the entire sector,which is formed by the forming sector FS and the draining sector ES,does not necessarily coincide with the double-screen segment ordouble-screen sector US. Also, the forming sector FS and the drainingsector ES do not necessarily coincide with certain suctioning sections.The point E is located in FIG. 1 in the suctioning section 32.

The double-screen segment US extends, as noted at the outset, over thatsector in which the two screens are guided approximately parallel to oneanother. In any case, the outer screen is lifted from the combinationroll 22 after the point E, and in fact, by means; of a screen guideroll. Depending upon the application, the outer screen can be liftedfrom the combination roll 22, just after point E, in the vicinity of theend of the last suctioning section or between. To this end, the guidingroll is preferably constructed to be adjustable (not depicted in moredetail).

The inner screen 16 loops around the combination roll 22, preferably upto the end of the last suctioning section 36, as it is shown in FIG. 1.

The suctioning sections 30 through 36 are separated from each other bypacking strips 37, in order to construct an adjustable, different vacuumpressure at each of the suctioning sections.

On the outer screen 18, a multiplicity of forming strips 38 is locatedin the forming sector FS (four in the illustration, as an example),which are arranged in the direction of the running screen behind oneanother. The forming strips 38 are constructed as elastically flexiblestrips. A large portion of the strips (in the present case, three) isarranged opposite the first suctioning section 30. The remaining formingstrips 38 (presently, one) are arranged opposite the second suctioningsection 32. A stiff, water-reversal strip which does not touch the outerscreen can be arranged in front of the first forming strip in thedirection of the running screen, as is shown schematically in FIG. 1.The last forming strip 38 is arranged before point E, in any case. As isshown in FIG. 1, the forming strips can be mounted together with thereversal strip to a yoke 39 which is linked to a stationary hinge andwhich can be pressed against the combination roll 22.

The suctioning sections 30, 32, 34, and 36 are connected to aschematically depicted suctioning unit 40.

The suctioning unit 40 exhibits a bearing pipe which is concentric tothe jacket of the combination roll 22 and which is connected on bothfront ends of the combination roll 22—that is, both on the lead side aswell as on the drive side—to a corresponding blower (not depicted) inorder to be able to produce the necessary vacuum at the suctioningsections 30, 32, 34, 38. The suctioning unit 40 is explained below withgreater precision using FIG. 7.

The jacket 41 of the combination roll 22 is designed as a perforatedroll jacket 60 and covered with a honeycomb covering 58. The watersuctioned up via the suctioning sections 30 through 36 is stored in thehoneycomb covering 58 and in the holes of the roll jacket 60.

A water collection chamber 42 is arranged in the area of a peripheralsection of the combination roll 22 following the last suctioning section36. The water stored in the jacket 41 of the combination roll is spunfrom the jacket 41 in the vicinity of this peripheral section, due tothe appearing centrifugal forces, and collected in the collection box42, and diverted, if necessary.

Across from the three draining suctioning sections 30, 32, 34, anothercollection box 44 is arranged on the outer screen 18, in order tointercept, to collect, and, if necessary, to divert water escaping fromthe outer screen 18.

A guiding roll 46 is arranged in the direction of the running screenbehind the combination roll 22. The inner screen 16 is wrapped aroundthe guiding roll 46. At the same time, the guiding roll 46 can besuctioned, as is shown schematically with 47.

Behind the guiding roll 46, another guiding roll 48 is arranged; betweenthe two guiding rolls 46, 48, a flat suction box 50 can be arranged.

On a suctioned take-up roll 52, the fibrous material web is taken fromthe inner screen 16 onto a belt 54 and transferred into another sectionof the paper machine.

In FIG. 1, other guiding rolls are shown but not in more detail. Theseguiding rolls serve the completion of the screen circuits and can beadjusted according to demand. It is given that all elements of the wetsection 10 are constructed according to the width of the machine, if nototherwise noted.

During operation, the relatively thin fluid fibrous material suspension27 is introduced by means of the head box 12 into the opening 26. Inorder to suction water through the inner screen 16 into the jacket 41 ofthe combination roll, a relatively low vacuum suffices in the firstsuctioning section 30.

In the following suctioning sections 32 and 34, a larger suctioningcapacity is needed, on the one hand to still remove water from thefibrous material suspension or web and, on the other hand, to keep thealready-removed water in the jacket 41 of the combination roll 22.

In the area of the first and the second suctioning sections 30, 32, theinitial draining for the immobilization of the fibrous materialsuspension 56 occurs up to point E. Through the forming strip 38, whichis arranged on the outer screen 18, it is guaranteed that a good“formation,” i.e., an even distribution of fibers, and a uniform crossdirectional profile of the fibrous material web are attained. In thevicinity of the other suctioning sections, 34, 36, another draining ofthe formed fibrous material web occurs.

At the end of the third suctioning section 34, the outer screen 18separates itself from the formed fibrous material web. The fibrousmaterial web remains secure on the inner screen 16, due to thesuctioning sections 34, 36. The inner screen 16 is transferred to theguiding roll 46 from the combination roll 22 at the end of the fourthsuctioning section 38.

The water stored in the jacket 41 of the combination roll 22 is spun outbehind the fourth suctioning section 36 radially due to the centrifugalforces and collected by the box 42.

It is given that both the suctioning section 47 of the guiding roll 46as well as the flat suction box 50 are not necessary as defined by theinvention. They can, however, be provided according to demand and incertain applications.

Overall, the suctioning unit 40 produces a very high air flow volume.Because this air flow volume is diverted via the bearing pipe ofrelatively large diameter and to both front ends of the combination roll22, the velocity of the air flow volume can be kept low.

It is given that cleaning devices can be assigned to the screens 16, 18.Furthermore, constructing the wet section 10 in the so-called “cleandesign” is preferred, whereby closed and suctioned screen chambers arepresent in the vicinity of the draining zones.

It is especially preferred that the wet section 10 is used for themanufacture of graphics paper about with 30 to 110 g/m².

In FIG. 3, shown in schematic form is a head box 12 which isconsistency-controlled and which is suited for the control of the crossdirectional profile with different characteristics of the fibrousmaterial web, especially of the cross directional profile basis weightand fiber-orientation. The fibrous material suspension 27 is supplied indilutions which can be regulated sectionally by means of a large numberof dilution-water control valves 61 which are arranged in distributionover the machine width. At the same time:, the mixer structure isarranged advantageously such that each of the sectional volume flowsremains constant with a local change of the dilution; see patent DE 4019 593.

Further forms of the embodiment of a wet section in accordance with theinvention are generally noted by 10A in FIG. 4, by 10B in FIG. 5, by 10Cin FIG. 6, by 10D in FIG. 8, by 10E in FIG. 9, and by 10F in FIG. 10.

Elements with identical function such as corresponding elements of thewet section 10 from FIG. 1 are fitted with identical referentialnumbers. Thereafter, therefore, only the differences from the wetsection 10 will be discussed.

The combination roll 22A of the wet section 10A exhibits a diameterwhich is comparatively even greater than the combination roll 22 of FIG.1 Moreover, the combination roll 22A is not driven. The drive of theinner screen 16 ensues via one of the guiding rolls in the inner screen16, in the present case a guiding roll 62.

In contrast to the wet section 10 of FIG. 1, the outer screen 18 islifted from the fibrous material web almost directly behind the point E,so that the sector angle of the double-screen segment US is notsignificantly greater than the angle of the forming sector FS.

Furthermore, between the combination roll 22A and the take-up roll 52,no other suctioned roll is provided. The inner screen 16 is guidedbetween the combination roll 22A and the take-up roll 52 only via thediversion roll 48.

A suctioning box 50A is provided between the combination roll 22A andthe diversion roll 48. The suctioning box 50A is provided in an integralmanner with the collection box 42, in such a manner that an outer wallof the suctioning box 50A simultaneously forms a wall of the collectionbox 42 at the same time. This is especially advantageous, since in thisway, water clinging to the screen 16 or on the underside of the fibrousmaterial web dripping on the machine parts located underneath isavoided.

In FIG. 4, moreover, it is shown in 64′ that a roll 64 is driven andadjustable, by means of which the outer screen 18 is lifted from thefibrous material web, in order to be able to influence the length of thedouble-screen segment US.

The forming strip yoke 39A is designed to be adjustable in height, incontrast to the forming strip yoke 39 of FIG. 1, which is shownschematically by an arrow, in order to be able to undertake changes invarious consistencies of the fibrous material suspension in a simplemanner. The roll 64 is designed to also be adjustable, in order to beable to guarantee that the outer screen 18 is lifted from the fibrousmaterial web only after the point E, even with fibrous materialsuspensions which are difficult to drain. In addition, the possibilityexists to execute the later draining in the draining sector ES at leastpartially with the covering of the web by the outer screen 18.

Another form of the embodiment of a wet section in accordance with theinvention is noted generally by 10B in FIG. 5.

In contrast to the wet section 10 of FIG. 1, the inner screen 16B isfastened to the combination roll 22B as a fine-meshed “screen stocking,”without running over other rolls.

Another suctioning section 65 is provided connected the suctioningsection 36, the suctioning section 65 that serves to keep the water inthe jacket 41 of the combination roll 22B. The suctioning section 65extends from the suctioning section 36 to a point at which a suctionedtake-up roll 52B transfers the fibrous material web onto a belt 54 fromthe jacket-like inner screen 16B. Following the suctioning section 65,the water found in the jacket 41 of the combination roll 22B is spun outinto a collection box. In order to make the transfer of the web from therelatively stiff jacket of the combination roll 22B easier, the take-tiproll 52B has a soft covering 52′.

Another form of the embodiment of the wet section in accordance with theinvention is generally referred to in FIG. 6 as 10C.

In contrast to the wet section 10 of FIG. 1, the outer screen 18 isguided around a shoe press roll 66, which forms an extended-nip pressopening (press nip) together with the combination roll 22C in thevicinity of the last suctioning section 36. The shoe press roll 66 has athin, flexible roll jacket and a press shoe with a concave runningsurface in a known manner. In FIG. 6, the roll 22C has the function of acombined forming, draining, and press roll. In this form of theembodiment, the formed fibrous material web can be transferred directlyfrom the inner screen onto a belt of the drying section.

It is given that even in the wet section 10, collection boxes for watercan be provided and that the jacket of the combination roll 22C can beconstructed as a reservoir for the water taken from the fibrous materialsuspension.

FIG. 7 shows a longitudinal section in largely schematic form, throughthe non-driven combination roll 22A of FIG. 4. At the same time, thecross-section runs through the suctioning section 30, for example, whichis connected to the suctioning unit 40-1. The other suctioning sections34, 36 are connected to the suctioning units 40-2 and 40-3,respectively.

It is to be recognized that the air flow volumes thus are diverted overboth front ends of the combination roll 22A. In all cases, the entiresuctioning cross-section is comparatively large. If needed, one canprovide a bearing pipe with a larger suctioning cross-section at onefront end (in FIG. 7, right) than at the other front end. This can makeeasier the arrangement of a drive for the combination roll 22A (at theleft front end in FIG. 7), in the event that a drive is necessary.

In FIG. 8, another embodiment of the wet section in accordance with theinvention is shown, which is generally referred to as 10D.

In contrast to the wet section 10B of FIG. 5, a shoe press roll 66D isprovided in place of the take-up roll 52B. The shoe press roll 66D isarranged in a felt 68, by means of which the fibrous material web isremoved from the inner screen 16B. This embodiment therefore possesses acomparatively simple construction. The felt 68 of the shoe press roll66D serves at the same time as take-up felt for the continued conveyanceof the fibrous material web.

Another embodiment of the wet section in accordance with the inventionis generally referred to as 10E in FIG. 9.

In contrast to the wet section 10D of FIG. 8, a shoe press roll 66E isarranged in a separate felt 70, which is lifted quickly from the fibrousmaterial web behind the shoe press roll 66E by means of a roll 72. Thefibrous material web remains on the inner screen 16B, therefore, and islifted by means of a take-up roll 52E from the inner screen, theconstruction of which corresponds to the take-up roll 52B of FIG. 5.

In this embodiment, in contrast to the wet section 10D of FIG. 8, theremoistening of the fibrous material web behind the shoe press roll 66Efrom the felt can be hindered. This is because the felt 70 is taken updirectly from the fibrous material web behind the shoe press roll 66E.

Finally, another embodiment of the wet section in accordance with theinvention is generally noted by the number 10F in FIG. 10. In contrastto the wet sections 10 through 10E shown previously, the head box 10F isarranged so that the fibrous material suspension flows from above tobelow. The fibrous material suspension flows into an opening which isformed by the combination roll 22F and an outer screen 18F. Thecombination roll 22F can, similar to the forming roll 22B, be coveredwith a fine-meshed “screen stocking” (not shown). The double-screensegment extends with the wet section 10F over almost 180°, with a row offorming strips 38F being again provided in a first part of thedouble-screen segment. The forming strips are located essentially in alower section of the combination roll 22F, so that the water escapingvia the outer screen 18F can be collected in a simple manner by a watercollection box 44F.

In a second sector of the double-screen segment located subsequent tothat, a shoe press roll 66F is provided, which is arranged in acirculating felt 70F. After the runoff of the outer screen 18F from thefibrous material web, the fibrous material web is removed from thecombination roll 22F by means of a suctioned take-up roll 52F andtransferred to another section of the paper machine.

It is self-evident that in an upper segment of the combination roll 22F,that is behind the take-up roll 52 F, a vacuum chamber must be provided,in order to safely absorb water which has been stored in the roll jacketof the combination roll 22F and spun upward.

In the wet sections 10, 10A, 10B, 10C, 10D, 10E, 10F, the screens 16, 18can be replaced by felts or by a felt/screen combination.

The head box 12 can be a consistency-controlled head box in all cases,as is shown in FIG. 3, in order to be able to control the crossdirectional profile of the fibrous material web.

What is claimed is:
 1. A wet section of a machine for the manufacture ofa fibrous material web comprising: a double-screen segment comprisingtwo screens being guided approximately parallel to one another and intowhich a fibrous material suspension is introduced; and a roll aroundwhich said double-screen segment is looped, said roll being a combinedforming and draining roll, said roll comprising: a multitude ofsuctioning sections, located on an outer surface of said roll, saidmultitude of suctioning sections further subdivided into a formingsector and a draining sector; said forming sector comprising a firstsuctioning section and a second suctioning section extending over asector of the roll from 20° to 100°, and said forming sector is arrangedto immobilize the fibrous material web within said forming sector; saiddraining sector, located in a screen run direction behind said formingsector, comprising a plurality of suctioning sections which comprise atleast a majority of suctioning sections from said multitude ofsuctioning sections, wherein said plurality of suctioning sections ofsaid draining sector comprises a first suctioning section, a secondsuctioning section, and a third suctioning section extending overallover a sector of the roll from 60°-150°, the suctioning capacity of saiddraining sector becoming greater in the screen run direction fromsuctioning section to suctioning section, wherein continued draining ofthe fibrous material web takes place within said draining sector; one ofsaid two screens of said double-screen segment being an outer screen,said outer screen facing away from said roll being guided so that saidouter screen is lifted from the fibrous material web while in saiddraining sector.
 2. The wet section of a machine according to claim 1,one fibrous material web being one of a paper web and a cardboard web.3. The wet section of a machine according to claim 1, the fibrousmaterial web exhibiting a dry content of at least 10% in the vicinity ofits runoff from said roll.
 4. The wet section of a machine according toclaim 3, the fibrous material web exhibiting a dry content of at least12% in the vicinity of its runoff from said roll.
 5. The wet section ofa machine according to claim 1, the outer screen facing away from theroll being lifted from the fibrous material web by a screen guidingroll, said screen guiding roll being constructed so as to be adjustable,in order to adjust a length of said double-screen segment.
 6. The wetsection of a machine according to claim 1, the fibrous materialsuspension being introduced by a head box into said double-screensegment, said head box being arranged so that the fibrous materialsuspension flows out against the force of gravity.
 7. The wet section ofa machine according to claim 1, a vacuum pressure of 0.6-0.99 barabsolute being applied to the first suctioning section of said pluralityof suctioning sections of said draining sector, a vacuum pressure of0.3-0.7 bar absolute being applied to the second suctioning section ofsaid plurality of suctioning sections of said draining sector, and avacuum pressure of 0.2-0.4 bar absolute being applied to the thirdsuctioning section of said plurality of suctioning sections of saiddraining sector.
 8. The wet section of a machine according to claim 1,wherein the first suctioning section, the second suctioning section, andthe third suctioning section of the draining sector extend overall overa sector of the roll from 70°-90°.
 9. The wet section of a machineaccording to claim 1, a vacuum pressure of 0.7 to 0.99 bar absolutebeing applied to the first suctioning section of said forming sector.10. The wet section of a machine according to claim 1, a jacket of saidroll being constructed as a reservoir for water extracted from at leastone of the fibrous material suspension and the fibrous material web. 11.The wet section of a machine according to claim 10, said roll beingequipped with a suctioning unit which produces an air volume flow whichis sufficient to suction essentially all the water which is extractedthrough an inner screen from at least one of the fibrous materialsuspension and the fibrous material web into said jacket of the roll.12. The wet section of a machine according to claim 11, said suctioningunit diverting the air volume flow to both front ends of the roll. 13.The wet section of a machine according to claim 1, said roll notexhibiting its own drive.
 14. The wet section of a machine according toclaim 1, at least one forming strip, which may be pressed against anouter screen facing away from said roll in a flexible manner, beingarranged in said forming sector.
 15. The wet section of a machineaccording to claim 14, said at least one forming strip being arranged onsaid outer screen opposite said forming sector of said roll.
 16. The wetsection of a machine according to claim 14, a row of about 3 to 15forming strips being arranged over said forming sector in distribution.17. The wet section of a machine according to claim 14, a row of about 5to 8 forming strips being arranged over said forming sector indistribution.
 18. The wet section of a machine according to claim 1, awater collection box being arranged on said outer screen facing awayfrom said roll, said water collection box extending over said entiredouble-screen segment.
 19. The wet section of a machine according toclaim 18, another water collection box being arranged on a peripheralsection of said roll which is located behind the draining sector. 20.The wet section of a machine according to claim 19, wherein saidcollection box and said another water collection box are arranged suchthat the water is collected essentially due to the force gravity alone.21. The wet section of a machine according to claim 1, the diameter ofsaid roll being greater than 1.5 m.
 22. The wet section of a machineaccording to claim 1, the diameter of said roll being greater than 2 m.23. The wet section of a machine according to claim 1, at least oneextended-nip press device in said draining sector being arranged on saidouter belt, which is facing away from said roll.
 24. The wet section ofa machine according to claim 23, said at least one extended-nip pressdevice exhibiting a shoe press roll, a mating roll of which is saidroll.
 25. The wet section of a machine according to claim 24, said outerscreen being looped around said shoe press roll, such that it is liftedfrom the fibrous material web.
 26. The wet section of a machineaccording to claim 24, said shoe press roll being arranged behind saiddouble-screen segment on said roll with respect to the screen rundirection.
 27. The wet section of a machine according to claim 26, abelt being looped around said shoe press roll, the fibrous material webbeing removed from an inner screen of the double-screen segment, theinner screen facing said roll.
 28. The wet section of a machineaccording to claim 26, a belt being looped around said shoe press roll,said belt being removable from the fibrous material web just behind saidshoe press roll, the fibrous material web behind said shoe press rollbeing removable from an inner screen of the double-screen segment, theinner screen facing said roll.
 29. The wet section of a machineaccording to claim 23, no further press devices being provided between arunoff point of the fibrous material web from said roll and a transferpoint to a drying section.
 30. A process for the manufacture of afibrous material web comprising: guiding two screens in a double-screensegment parallel to each other and around a roll comprising a multitudeof suctioning sections located on an outer surface of said roll, one ofsaid two screens being an outer screen facing away from said roll;introducing a fibrous material suspension into the double-screensegment; immobilizing the fibrous material suspension on the roll in thedouble-screen segment for the formation of a fibrous material web, theimmobilization occurring in a forming sector of the roll, said formingsector comprising a first suctioning section and a second suctioningsection extending over a sector of the roll from 20° to 100°; drainingthe fibrous material web further, at least a predominant part of thedraining occurring in a draining sector of the roll, the draining sectorbeing located in a screen run direction behind the forming sector, saiddraining sector comprising a plurality of suctioning sections whichcomprise at least a majority of suctioning sections from said multitudeof suctioning sections, wherein said plurality of suctioning sections ofsaid draining sector comprises a first suctioning section, a secondsuctioning section, and a third suctioning section extending overallover a sector of the roll from 60°-150°, the suctioning capacity of saiddraining sector becoming greater in the screen run direction fromsuctioning section to suctioning section; and guiding said outer screenso that the outer screen is lifted from the fibrous material web whilein said draining sector.
 31. The process according to claim 30, thefibrous material web comprising one of a paper web and a cardboard web.32. The process according to claim 30, comprising manufacturing graphicpapers with a basis weight of about 30 to 110 g/m².